20 THE VETERINARY SCIENCE. 



strained it is the seat of what is called thoroughpin. It then 

 passes down the back part of the shin bone beneath the other 

 tendon already mentioned, through the loop at the fetlock to the 

 back part of the foot bone, where it is attached. The action of 

 these muscles are to flex or bend the fetlock and raise the hock joint 

 in travelling. 



Involuntary Muscles, or muscles which are not under the 

 control of the will. The first we call attention to are the muscles 

 of breathing, • or respiration ; they are a group situated around 

 the chest in such a way as to enlarge the chest cavity and 

 draw the air into the lungs — this action is called inspiration — while 

 others in acting decreases the size of the chest cavity and forces 

 the air out of the lungs, which is called expiration. The diaphragm 

 is a muscular curtain which separates the chest from the abdominal 

 cavity, and also assists greatly in drawing the air in, when it 

 contracts ; this muscle also assists in passing manure, and in the 

 mare foaling. It separates the heart and lungs from the bowels, 

 liver and stomach. Everyone interested should examine this 

 muscle, which can be seen by opening any dead animal. 



There is one muscle which is both voluntary and involuntary. 

 It is situated in the penis, surrounding the urethra, or the tube, 

 which carries the urine from the bladder to the penis in the male 

 animal. Its action is voluntary while the animal is passing urine, 

 or water. It acts involuntary during sexual intercourse, forcing 

 the semen down through the penis. There is what is known by 

 the name of fat situated between the muscles. 



CHAPTER IV. 



THE NERVOUS SYSTEM. 



THIS system is a very important set of organs which give 

 motion and feeling to the body, and the different senses, 

 such as seeing, hearing, smelling and tasting. The two 

 principal parts of the nervous system are the brain and spinal 

 cord. The brain, being the centre of the whole nervous system, 

 is situated in the cranial cavity, surrounded by three delicate 

 membranes, the outer one being attached to the inner wall of the 

 cranial cavity. The brain contains several important nerves 

 called the cranial nerves, which are given off from the brain and 

 passed down through the various foramen or openings in the 



